I had to remove 6 layers of wallpaper, with paint in between layers, from my house when I moved in. After about 2 hours and very little progress, I gave-in and decided to pay someone who strips wallpaper for a living. It was worth every penny ($400 for two large rooms) - it took the guy 4 days. With all the other work I had to do, I was glad to have someone else take care of it.
But if you must do it yourself.. a wide razor scraper and a few gallons of hot vinegar will get you going. Be careful not to gouge the walls too much.
Whatever you do, don't drywall over it - it will cost much more - and you didn't buy an 80 year old house because you like perfect, drywall walls - right? (You're going to have cracks in the plaster - so what?)